Insulation detection circuit and method, and battery management system

ABSTRACT

The present disclosure provides an insulation detection circuit and method, and a battery management system. The circuit includes a first isolation module, a voltage division module, a signal generation module, first and second sampling points and a processor. A first end of the first isolation module is connected to a power battery, and a second end of the first isolation module is connected to the second sampling point. The signal generation module is connected to the first sampling point and configured to inject an AC signal into the power battery and provide the first sampling point with a first sampled signal. A first end of the voltage division module is connected to the first sampling point, and a second end of the voltage division module is connected to the second sampling point. The processor is configured to calculate an insulation resistance of the power battery.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 16/245,198, filed on Jan. 10, 2019, which claims priority toChinese Patent Application No. 201810102891.X, filed on Feb. 1, 2018.The aforementioned patent applications are hereby incorporated byreference in their entireties.

FIELD

The present disclosure relates to the field of batteries, particularlyto an insulation detection circuit and method, and a battery managementsystem.

BACKGROUND

A power battery is responsible for storing and supplying electricenergy. In use, it is necessary to design an insulation detectioncircuit to monitor in real time whether an insulation resistance of anentire high voltage system of an electric vehicle (including theinsulation resistance of a power battery pack and the entire vehicle)meets a standard, so as to avoid high voltage safety issues caused inthe case that the insulation resistance of the high voltage system ofthe electric vehicle does not meet the standard.

In order to detect the insulation resistance of the power battery, aconventional insulation detection circuit needs to directly inject ahigh-frequency AC (Alternating Current) signal into the power battery,connect one end of the high-frequency AC signal to the ground or a bodyof the vehicle, and then calculate the insulation resistance accordingto acquired signals.

However, inventors of the present application found that when using theexisting method of injecting the high-frequency signal, the detectionresult of the insulation resistance is usually impacted by a parasiticcapacitance of the power battery under detection, resulting in a largedetection error of the insulation resistance.

SUMMARY

A battery management system and an insulation detection method areprovided in the embodiments of the present disclosure.

In a first aspect of the present disclosure, a battery management systemis provided and includes an insulation detection circuit, including afirst isolation module, a voltage division module, a signal generationmodule, a first sampling point and a second sampling point, wherein afirst end of the first isolation module is connected to a positiveelectrode of a power battery under detection, a second end of the firstisolation module is connected to the second sampling point, the signalgeneration module is connected to the first sampling point, a first endof the voltage division module is connected to the first sampling point,and a second end of the voltage division module is connected to thesecond sampling point; a memory configured to store computer codes; aprocessor configured to execute the computer codes to: acquire a firstsampled signal from the first sampling point and acquire a secondsampled signal from the second sampling point when a preset condition issatisfied, wherein the preset condition is the signal generation modulegenerates an AC voltage signal of a predetermined frequency; andcalculate an insulation resistance of the power battery under detectionaccording to the first sampled signal and the second sampled signal.

In an implementation of the first aspect, the processor is further to:obtain a first voltage amplitude and a bias voltage of the first sampledsignal and a second voltage amplitude of the second sampled signal, andobtain a first instantaneous voltage of the first sampled signal and asecond instantaneous voltage of the second sampled signal at a samemoment; calculate a phase shift of the second sampled signal relative tothe first sampled signal according to the first voltage amplitude, thebias voltage, the first instantaneous voltage, the second voltageamplitude, and the second instantaneous voltage; and calculate theinsulation resistance of the power battery under detection according tothe phase shift, the first voltage amplitude, and the second voltageamplitude.

In an implementation of the first aspect, the processor is further to:obtain the first instantaneous voltage at a rising edge of a waveform ofthe first sampled signal and the second instantaneous voltage at arising edge of a waveform of the second sampled signal at the samemoment.

In an implementation of the first aspect, the processor is further to:calculate the insulation resistance of the power battery under detectionaccording to the phase shift, the first voltage amplitude, the secondvoltage amplitude, the predetermined frequency, a capacitance value ofthe first isolation module and a resistance value of the voltagedivision module.

In an implementation of the first aspect, the processor is further tore-determine whether the preset condition is satisfied after apredetermined time period, when the preset condition is not satisfied.

In an implementation of the first aspect, the signal generation moduleis a DDS waveform generator.

In an implementation of the first aspect, the AC voltage signal is asine wave voltage signal.

In an implementation of the first aspect, the predetermined frequency isless than or equal to 50 kHz.

In an implementation of the first aspect, the battery management systemof claim further includes a signal amplification module configured toincrease a voltage amplitude of the AC voltage signal.

In a second aspect of the present disclosure, an insulation detectionmethod is provided to be applied to the above described batterymanagement system. The method includes acquiring a first sampled signalfrom the first sampling point and acquiring a second sampled signal fromthe second sampling point when a preset condition is satisfied, whereinthe preset condition is the signal generation module generates an ACvoltage signal of a predetermined frequency; and calculating aninsulation resistance of the power battery under detection according tothe first sampled signal and the second sampled signal.

In an implementation of the second aspect, the calculating theinsulation resistance of the power battery under detection according tothe first sampled signal and the second sampled signal includes:obtaining a first voltage amplitude and a bias voltage of the firstsampled signal and a second voltage amplitude of the second sampledsignal, and obtaining a first instantaneous voltage of the first sampledsignal and a second instantaneous voltage of the second sampled signalat a same moment; calculating a phase shift of the second sampled signalrelative to the first sampled signal according to the first voltageamplitude, the bias voltage, the first instantaneous voltage, the secondvoltage amplitude, and the second instantaneous voltage; and calculatingthe insulation resistance of the power battery under detection accordingto the phase shift, the first voltage amplitude, and the second voltageamplitude.

In an implementation of the second aspect, the obtaining a firstinstantaneous voltage of the first sampled signal and a secondinstantaneous voltage of the second sampled signal at a same momentincludes: obtaining the first instantaneous voltage at a rising edge ofa waveform of the first sampled signal and the second instantaneousvoltage at a rising edge of a waveform of the second sampled signal atthe same moment.

In an implementation of the second aspect, the calculating theinsulation resistance of the power battery under detection according tothe phase shift, the first voltage amplitude, and the second voltageamplitude includes: calculating the insulation resistance of the powerbattery under detection according to the phase shift, the first voltageamplitude, the second voltage amplitude, the predetermined frequency,the capacitance of the first isolation module and the resistance of thevoltage division module.

In an implementation of the second aspect, the insulation detectionmethod further includes re-determining whether the preset condition issatisfied after a predetermined time period, when the preset conditionis not satisfied.

In an implementation of the second aspect, the AC voltage signal is asine wave voltage signal.

In an implementation of the second aspect, the predetermined frequencyis less than or equal to 50 kHz.

In an implementation of the second aspect, the insulation detectionmethod further includes increasing a voltage amplitude of the AC voltagesignal after the AC voltage signal is generated by the signal generationmodule.

In a third aspect of the present disclosure, a non-transitory computerreadable storage medium having programs or instructions stored thereonis provided. The programs or the instructions, when executed by aprocessor, perform the above described insulation detection method.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be better understood from the following description ofthe specific embodiments of the invention, taken in conjunction with theaccompanying drawings, in which like or similar reference numeralsindicate identical or similar features.

FIG. 1 is a schematic structural diagram of an insulation detectioncircuit according to a first embodiment of the present disclosure;

FIG. 2 is a schematic structural diagram of an insulation detectioncircuit according to a second embodiment of the present disclosure;

FIG. 3 is a schematic structural diagram of an insulation detectioncircuit according to a third embodiment of the present disclosure;

FIG. 4 is a schematic flow chart of an insulation detection methodaccording to a first embodiment of the present disclosure;

FIG. 5 is an equivalent circuit diagram of the insulation detectioncircuit corresponding to FIG. 3; and

FIG. 6 is a schematic flow chart of an insulation detection methodaccording to a second embodiment of the present disclosure.

DETAILED DESCRIPTION

The features and exemplary embodiments of various aspects of the presentdisclosure are described in detail below. In the following detaileddescription, numerous specific details are set forth in order to providea thorough understanding of the present disclosure.

The embodiments of the present disclosure provide an insulationdetection circuit and method, and a battery management system. With themethod of injecting an AC signal into a power battery under detection,the insulation detection circuit can separately process a detected sinewave voltage signal from a signal generation module and a detected sinewave voltage signal between an isolation module and a voltage divisionmodule to obtain the insulation resistance of the power battery underdetection, thus resulting in an improved detection accuracy of theinsulation resistance.

It should be noted that the power battery under detection in theembodiments of the present disclosure may be a lithium-ion battery, alithium-metal battery, a lead-acid battery, a nickel-cadmium battery, anickel-metal hydride battery, a lithium-sulfur battery, a lithium-airbattery, or a sodium-ion battery, which is not limited herein. In termsof scale, the power battery under detection can be a single cell or abattery module or a battery pack, which is not limited herein either.

The battery management system includes the above insulation detectioncircuit. For example, the above insulation detection circuit may beintegrated in the battery management system.

FIG. 1 is a schematic structural diagram of an insulation detectioncircuit according to a first embodiment of the present disclosure. Asshown in FIG. 1, the insulation detection circuit includes a firstisolation module G1, a voltage division module F1, a signal generationmodule Y1, a first sampling point S1, a second sampling point S2 and aprocessor P1.

A first end of the first isolation module G1 is connected to a positiveelectrode of the power battery under detection, and a second end of thefirst isolation module G1 is connected to the second sampling point S2.The first isolation module G1 may be configured to isolate ahigh-voltage signal of the power battery under detection frominterfering with a low-voltage sampled signal.

The signal generation module Y1 is connected to the first sampling pointS1. The signal generation module Y1 may be configured to inject an ACsignal of a predetermined frequency into the power battery underdetection and provide the first sampling point S1 with a first sampledsignal of a predetermined frequency.

A first end of the voltage division module F1 is connected to the firstsampling point S1, and a second end of the voltage division module F1 isconnected to the second sampling point S2. The voltage division moduleF1 may be configured to provide the second sampling point S2 with asecond sampled signal, which is the sampled signal for the secondsampling point S2 at the voltage division module F1.

The processor P1 may be configured to calculate the insulationresistance of the power battery under detection according to the firstsampled signal and the second sampled signal.

A positive electrode capacitor Cp, a negative electrode capacitor Cn, apositive electrode insulation resistor Rp and a negative electrodeinsulation resistor Rn of the power battery under detection are alsoshown in FIG. 1.

It can be understood that the positive electrode capacitor Cp and thenegative electrode capacitor Cn are equivalent capacitors of the powerbattery under detection relative to a low-voltage ground, the positiveelectrode insulation resistor Rp is the insulation resistor of thepositive electrode of the power battery under detection relative to thelow-voltage ground, and the negative electrode insulation resistor Rn isthe insulation resistor of a negative electrode of the power batteryunder detection relative to the low-voltage ground.

In the embodiment of the present disclosure, an AC voltage signalinjected by the signal generation module Y1 can be acquired from thefirst sampling point S1, and an AC voltage signal between the voltagedivision module F1 and the first isolation module G1 can be acquiredfrom the second sampling point S2. The AC voltage signal between thevoltage divider module F1 and the first isolation module G1 may beaffected by the insulation resistance of the power battery underdetection. Thus based on Kirchhoff's law, the insulation resistance ofthe power battery under detection can be calculated by a comparisonbetween the AC voltage signal at the first sampling point S1 and the ACvoltage signal at the second sampling point S2.

The embodiment of the present disclosure provides the insulationdetection circuit including the first isolation module G1, the voltagedivision module F1, the signal generation module Y1, the first samplingpoint S1 and the second sampling point S2. The first end of the firstisolation module G1 is connected to the positive electrode of the powerbattery under detection, and the second end of the first isolationmodule G1 is connected to the second end of the voltage division moduleF1. The first isolation module G1 can isolate the high-voltage signal ofthe power battery under detection from interfering with the low-voltagesampled signal. Compared with the conventional method of directlyinjecting a high frequency AC signal into the power battery underdetection, in the embodiment of the present disclosure, the high-voltagesignal of the power battery under detection can be isolated fromimpacting on a low-voltage sampling circuit, and thus the first sampledsignal obtained from the first sampling point S1 and the second sampledsignal obtained from the second sampling point S2 can be made moreaccurate and accordingly the detection accuracy of the insulationresistance can be improved.

In addition, since the insulation detection circuit in the embodiment ofthe present disclosure only needs to further include the first isolationmodule G1 which can be specifically implemented by an isolationcapacitor, it may have the advantage of low cost.

In addition, according to the embodiment of the present disclosure,since it is only needed to detect the AC voltage signal at the firstsampling point S1 and the AC voltage signal at the second sampling pointS2 in order to calculate the insulation resistance of the power batteryunder detection, the calculation speed can be fast, the time fordetecting the insulation resistance can be shortened and the stabilityof the system will not be impacted.

In some embodiments, the signal generation module Y1 can be a DirectDigital Synthesis (DDS) waveform generator. Stability and accuracy of afrequency of a signal from the DDS waveform generator can reach the samelevel as a reference frequency, and the frequency can be finely adjustedover a wide frequency range. A signal source designed in this way canwork in a modulation state, in which an output level can be adjusted toobtain an output of various waveforms, such as a triangular wave, asquare wave, and the like.

In other embodiments, the first sampled signal generated by the signalgeneration module Y1 may be a low-frequency AC signal. In other words, alow-frequency AC signal may be injected into the power battery underdetection. For example, the frequency may be less than or equal to 50kHz. In comparison to the high frequency AC signal being injected intothe power battery under detection, the low frequency AC signal is lessimpacted by the high-voltage signal of the power battery underdetection, so that the detection accuracy of the insulation detectioncircuit can be further improved.

As shown in FIG. 1, in some embodiments, the processor P1 may be furtherconfigured to output an enable control signal to the signal generationmodule Y1 in response to the desire of detecting the power battery underdetection, so as to perform an automatic control to enable or disablethe insulation detection circuit.

FIG. 2 is a schematic structural diagram of an insulation detectioncircuit according to a second embodiment of the present disclosure. FIG.2 differs from FIG. 1 in that FIG. 2 shows components of the voltagedivision module F1 and the first isolation module G1. The specificstructures of the voltage division module F1 and the first isolationmodule G1 will be illustrated below by way of examples.

The voltage division module F1 may include a voltage division resistorR1. A first end of the voltage division resistor R1 is connected to thefirst sampling point S1, and a second end of the voltage divisionresistor R1 is connected to the second sampling point S2. The voltagedivision resistor R1 can function as a voltage divider. A variationrange of the sampled signal at the second sampling point S2 can beadjusted by changing the resistance of the voltage division resistor R1.

The first isolation module G1 may include an isolation capacitor C1. Afirst end of the isolation capacitor C1 is connected to the positiveelectrode of the power battery under detection, and a second end of thefirst isolation capacitor C1 is connected to the second sampling pointS2. The isolation capacitor C1 can isolate high voltages at the powerbattery side from low-voltage sampled signals. In addition, by changingthe capacitance of the isolation capacitor C1, the isolation effectbetween high voltages at the power battery side and a low-voltagesampling circuit can be adjusted.

FIG. 3 is a schematic structural diagram of an insulation detectioncircuit according to a third embodiment of the present disclosure. FIG.3 differs from FIG. 2 in that the insulation detection circuit shown inFIG. 3 further includes a first sampling circuit D1 and a secondsampling circuit D2. In the embodiment of the present disclosure, theprocessor P1 may directly acquire an AC signal from the first samplingpoint S1 or the second sampling point S2, or may acquire the AC signalfrom the first sampling point S1 or the second sampling point S2 via adedicated sampling circuit.

A first end of the first sampling circuit D1 is connected to the firstsampling point S1, and a second end of the first sampling circuit D1 isconnected to the processor P1. The first sampling circuit D1 may beconfigured to acquire the first sampled signal from the first samplingpoint D1.

A first end of the second sampling circuit D2 is connected to the secondsampling point S2, and a second end of the second sampling circuit D2 isconnected to the processor P1. The second sampling circuit D2 may beconfigured to acquire the second sampled signal from the second samplingpoint S2. A person skilled in the art can select an appropriate samplingcircuit based on practical needs, which is not limited herein.

In the example of FIG. 3, the insulation detection circuit may furtherinclude a second isolation module G2 and a third isolation module G3.

A first end of the second isolation module G2 is connected to the firstsampling point S1, and a second end of the second isolation module G2 isconnected to the first sampling circuit D1. The second isolation moduleG2 may be configured to isolate signal interference of the firstsampling circuit D1 on the first sampling point S1.

Specifically, the second isolation module G2 may include a first voltagefollower A1. A first input terminal of the first voltage follower A1 isconnected to the first sampling point S1, and a second input terminal ofthe first voltage follower A1 is connected to an output terminal of thefirst voltage follower A1. With the first voltage follower A1, thesignal interference of the first sampling circuit D1 on the firstsampling point S1 can be isolated.

A first end of the third isolation module G3 is connected to the secondsampling point S2, and a second end of the third isolation module G3 isconnected to the second sampling circuit D2. The third isolation moduleG3 may be configured to isolate signal interference of the firstsampling circuit D2 on the first sampling point S2.

Specifically, the third isolation module G3 includes a second voltagefollower A2. A first input terminal of the second voltage follower A2 isconnected to the second sampling point S2, and a second input terminalof the second voltage follower A2 is connected to an output terminal ofthe second voltage follower A2. With the second voltage follower A2, thesignal interference of the second sampling circuit D2 on the secondsampling point S2 can be isolated.

In the example of FIG. 3, the insulation detection circuit may furtherinclude a signal amplification module K1. A first input terminal of thesignal amplification module K1 is connected to the signal generationmodule Y1, a second input terminal of the signal amplification module K1is connected to an output terminal of the signal amplification moduleK1, the output terminal of the signal amplification module K1 isconnected to the first sampling point S1, and the second input terminalof the signal amplification module K1 is further connected to areference voltage terminal GND.

In the embodiment of the present disclosure, a voltage amplitude of theAC signal generated by the signal generation module Y1 can be adjustedvia the signal amplification module K1. For example, when the voltageamplitude of the AC signal generated by the signal generation module Y1is small, the voltage amplitude of the AC signal may be increased, so asto avoid the problem of low accuracy of the insulation detection due toa very low voltage amplitude of the AC signal.

Specifically, the signal amplification module K1 may include a signalamplifier B, a first amplification resistor R2, a second amplificationresistor R3, and a third amplification resistor R4. A first inputterminal of the signal amplifier B is connected to the signal generationmodule Y1, and the first amplification resistor R2 is located on a linebetween the first input terminal of the signal amplifier B and thesignal generation module Y1. A second input terminal of the signalamplifier B is connected to an output terminal of the signal amplifierB, and the second amplification resistor R3 is located on a line betweenthe second input terminal of the signal amplifier B and the outputterminal of the signal amplifier B. The output terminal of the signalamplifier B is connected to the first sampling point S1. The secondinput terminal of the signal amplification module K1 is furtherconnected to the reference voltage terminal GND, and the thirdamplification resistor R4 is located on a line between the second inputterminal of the signal amplification module K1 and the reference voltageterminal GND.

The embodiments of the present disclosure further provide a batterymanagement system, which includes the insulation detection circuit asdescribed above.

In the embodiments of the present disclosure, based on the aboveinsulation detection circuit, the insulation resistance of the powerbattery under detection can be calculated according to the first sampledsignal and the second sampled signal. The process of calculating theinsulation resistance of the power battery under detection based on theabove-mentioned insulation detection circuit according to theembodiments of the present invention will be described in detail below.

FIG. 4 is a schematic flow chart of an insulation detection methodaccording to a first embodiment of the present disclosure, which isapplied in the insulation detection circuits as shown in FIG. 1 to FIG.3. The insulation detection method shown in FIG. 4 may include steps 401to 403.

In step 401, a first voltage amplitude and a bias voltage of the firstsampled signal are obtained, a second voltage amplitude of the secondsampled signal is obtained, and a first instantaneous voltage of thefirst sampled signal and a second instantaneous voltage of the secondsampled signal are obtained at a same moment.

Preferably, the first instantaneous voltage at a rising edge of thewaveform of the first sampled signal and the second instantaneousvoltage at a rising edge of the waveform of the second sampled signalmay be obtained at the same moment to improve the calculation accuracyof phase shifts and accordingly increase the insulation detectionaccuracy.

In step 402, a phase shift of the second sampled signal relative to thefirst sampled signal is calculated according to the first voltageamplitude, the bias voltage, the first instantaneous voltage, the secondvoltage amplitude, and the second instantaneous voltage.

In step 403, the insulation resistance of the power battery underdetection is calculated according to the phase shift, the first voltageamplitude, and the second voltage amplitude.

Specifically, the insulation resistance of the power battery underdetection can be calculated according to the phase shift, the firstvoltage amplitude, the second voltage amplitude, the predeterminedfrequency, the capacitance of the first isolation module G1, and theresistance of the voltage division module F1.

To facilitate understanding by those skilled in the art, the process ofcalculating the insulation resistance of the power battery underdetection based on the above-mentioned insulation detection circuitaccording to embodiments of the present invention will be described indetail below.

Referring to FIG. 5, since the power battery under detection has a verysmall internal resistance, the power battery can be considered asequivalent to a short circuit. That is, FIG. 3 is equivalent to FIG. 5.

In FIG. 5, Rnp is the resistance obtained by the parallel connection ofthe positive electrode insulation resistor Rp and the negative electrodeinsulation resistor Rn, that is, Rnp=Rn//Rp; and Cnp is the capacitanceobtained by the parallel connection of the positive electrode capacitorCp and the negative electrode capacitor Cn, that is, Cnp=Cn//Cp. Theobtained insulation resistance Rnp is smaller than the resistance of Rnor Rp. In the embodiments of the present invention, the insulationresistance Rnp can be used as a standard for measuring the insulationperformance.

The derivation process of the insulation resistance Rnp of the powerbattery under detection of the insulation detection circuit will bedescribed in detail with reference to FIG. 5.

According to series and parallel formulas, the equivalent impedance Znpof the parasitic capacitance Cnp and the insulation resistance Rnp ofthe power battery under detection can be expressed as:

$\begin{matrix}{{Znp} = \frac{Rnp \times ZCnp}{{Rnp} + {ZCnp}}} & (1)\end{matrix}$

Here, ZCnp is the capacitive reactance of the parasitic capacitance Cnp,and the equivalent impedance Znp can be expressed in a vector form as:

$\begin{matrix}{\frac{Rnp}{{w^{2} \times Cnp^{2} \times Rnp^{2}} + 1} - {\frac{w \times Cnp \times Rnp^{2}}{{w^{2} \times Cnp^{2} \times Rnp^{2}} + 1} \times j}} & (2)\end{matrix}$

Here, w is an angular frequency of a sine wave AC signal generated bythe signal generation module Y1, and j is the imaginary unit.

Assuming that the equivalent impedance of the parasitic capacitance Cnp,the insulation resistance Rnp and the isolation capacitor C1 is Znp1,according to Kirchhoff's law, voltage amplitudes of a sine wave ACsignal between the isolation capacitor C1 and the voltage divisionresistor (also referred to as a sampling resistor) R1 and the sine waveAC signal generated by the signal generation module Y1 (i.e., the sinewave AC signal provided by the second sampling point S2 and the sinewave AC signal provided by the first sampling point S1) have thefollowing relationship:

$\begin{matrix}{\frac{U}{u} = \frac{{Znp1} + {R1}}{Znp1}} & (3)\end{matrix}$

In the formula, U is the voltage amplitude of the sine wave AC signalgenerated by the signal generation module Y1 and u is the voltageamplitude of the sine wave AC signal between the isolation capacitor C1and the voltage division resistor R1.

According to Kirchhoff's law, the relationship between the equivalentimpedance Znp of the parasitic capacitance Cnp and the insulationresistance Rnp and the equivalent impedance Znp1 of the parasiticcapacitance Cnp, the insulation resistance Rnp and the isolationcapacitor C1 can be expressed as:

$\begin{matrix}{{Znp} = {{{Znp}\; 1} - \frac{1}{j \times w \times C1}}} & (4)\end{matrix}$

Assuming that the phase shift of the sine wave AC signal between theisolation capacitor C1 and the voltage division resistor R1 relative tothe sine wave AC signal generated by the signal generation module Y1 isθ, the sine wave AC signal between the isolation capacitor C1 and thevoltage division resistor R1 can be expressed in a vector form as:

u=u×cos(θ)+u×sin(θ)×j  (5)

In order to eliminate the phase shift θ, the phase shift θ can beconverted into an expression of measurable values. For example, it canbe assumed that the instantaneous voltage UA of the sine wave AC signalgenerated by the signal generation module Y1 can be expressed by thefollowing function of time:

UA=U×sin(w×t)+M  (6)

It can be assumed that the instantaneous voltage UB of the sine wave ACsignal between the isolation capacitor C1 and the voltage divisionresistor R1 at the same moment can be expressed by the followingfunction of time:

UB=u×sin(w×t+θ)+M  (7)

Here, M is the bias voltage, and t is the time. To improve thecalculation accuracy of the insulation resistance, it is desired tosimultaneously obtain the first instantaneous voltage at the rising edgeof the waveform of the first sampled signal as the UA and the secondinstantaneous voltage at the rising edge of the waveform of the secondsampled signal as the UB.

Combining formula (5)-formula (7), the following formula for calculatingthe phase shift θ can be derived:

$\begin{matrix}{\theta = {{a \times {\sin \left( \frac{{UB} - M}{u} \right)}} - {a \times {\sin \left( \frac{{UA} - M}{u} \right)}}}} & (8)\end{matrix}$

Combining formula (3), formula (4) and formula (8) and aftersimplification, the following formula can be derived:

$\begin{matrix}{{Znp} = {\frac{\begin{matrix}{U \times u \times R\; 1 \times} \\{{\cos (\theta)} - {u^{2} \times R\; 1}}\end{matrix}}{\begin{matrix}{U^{2} - {2 \times U \times}} \\{{u \times \cos (\theta)} + u^{2}}\end{matrix}} + {\left( {\frac{\begin{matrix}{U \times u \times} \\{R\; 1 \times {\sin (\theta)}}\end{matrix}}{\begin{matrix}{U^{2} - {2 \times U \times u \times}} \\{{\cos (\theta)} + u^{2}}\end{matrix}} + \frac{1}{w \times C\; 1}} \right) \times j}}} & (9)\end{matrix}$

Combining formula (2) and formula (9), the insulation resistance Rnp ofthe power battery under detection can be derived as follows:

$\begin{matrix}{{Rnp} = {\frac{\begin{matrix}{\left( {{U \times {\cos (\theta)}} - u} \right) \times} \\{u \times R\; 1}\end{matrix}}{\begin{matrix}{U^{2} - {2 \times U \times}} \\{{u \times \cos (\theta)} + u^{2}}\end{matrix}} \times \left\lbrack {\frac{\begin{pmatrix}\begin{matrix}\begin{matrix}{w \times C\; 1 \times U \times} \\{u \times R\; 1 \times}\end{matrix} \\{{\sin (\theta)} + U^{2} + u^{2} -}\end{matrix} \\{2 \times U \times u \times {\cos (\theta)}}\end{pmatrix}^{2}}{\begin{matrix}\begin{matrix}{w^{2} \times C1^{2} \times} \\{u^{2} \times R1^{2} \times}\end{matrix} \\\left( {{U \times {\cos (\theta)}} - u} \right)^{2}\end{matrix}} + 1} \right\rbrack}} & (10)\end{matrix}$

As described above, according to the embodiments of the presentinvention, only two sets of instantaneous voltages UA and UB of thefirst sampling point S1 and the second sampling point S2 at the samemoment need to be measured. Then based on Kirchhoff's law, the sine wavesignal acquired at the first sampling point S1 and the sine wave signalacquired at the second sampling point S2 can be processed, so as tocalculate the phase shift θ of the second sampling point S2 relative tothe first sampling point S1 and further obtain the insulation resistanceof the power battery under detection according to formula (10).

FIG. 6 is a schematic flow chart of an insulation detection methodaccording to a second embodiment of the present disclosure. Theinsulation detection method based on the above described insulationdetection circuit shown in FIG. 6 includes steps 601 to 607.

In step 601, the insulation detection circuit is powered on.

In step 602, a DDS waveform generator is enabled.

In step 603, it is determined whether the DDS waveform generatorgenerates a sine wave. If the DDS waveform generator generates a sinewave, then step 604 is executed; if the DDS waveform generator does notgenerate a sine wave, step 603 is performed again.

In step 604, a first voltage signal is acquired from the first samplingpoint S1 and stored, and a second voltage signal is acquired from thesecond sampling point S2 and stored.

In step 605, a voltage amplitude U and a bias voltage M of the firstvoltage signal and a voltage amplitude u of the second voltage signalare obtained, and an instantaneous voltage UA at a rising edge of thefirst voltage signal and an instantaneous voltage UB at a rising edge ofthe second voltage signal at a same moment are obtained.

In step 606, the above UA, UB, M, U and u are substituted into theformula (8) to derive the phase shift θ.

In step 607, the above U, u and θ are substituted into the formula (10)to derive the insulation resistance Rnp of the power battery underdetection.

It should be noted that the processor in the embodiments of the presentdisclosure may be a processor having an independent function, or may bea processor to be integrated into the battery management system, whichis not limited herein.

It should be noted that, each embodiment in the disclosure is describedin a progressive manner, the same or similar parts in variousembodiments may be referred to each other, and each embodiment focuseson differences from other embodiments. For the circuit embodiments,reference may be made to the description of the method embodiments. Theembodiments of the present disclosure are not limited to the specificsteps and structures described above and shown in the drawings. A personskilled in the art may make various changes, modifications, andadditions or change the order of steps after understanding the spirit ofthe embodiments of the present disclosure. Also, for the sake ofconciseness, the detailed description of those known methods ortechniques is omitted here.

The functional blocks shown in the block diagrams described above may beimplemented in hardware, software, firmware, or a combination thereof.When implemented in hardware, it may be, for example, an electroniccircuit, an application specific integrated circuit (ASIC), a suitablefirmware, a plug-in, a function card or the like. When implemented insoftware, elements of the embodiments of the present disclosure areprograms or code segments used to perform required tasks. The programsor code segments may be stored in a machine-readable medium ortransmitted over a transmission medium or a communication link via datasignals carried in carriers. The “machine-readable medium” may includeany medium capable of storing or transmitting information. Examples ofthe machine-readable medium include an electronic circuit, asemiconductor memory device, a ROM, a flash memory, an erasable ROM(EROM), a floppy disk, a CD-ROM, an optical disk, a hard disk, a fibermedium, a radio frequency (RF) link, and the like. The code segments maybe downloaded via a computer network, such as the Internet, an intranet,or the like.

The embodiments of the present disclosure may be implemented in otherspecific forms without departing from the spirit and essentialcharacteristics thereof. For example, the algorithms described in thespecific embodiments may be modified as long as the system architecturewill not depart from the basic spirit of the embodiments of the presentdisclosure. The present embodiments are therefore to be considered inall respects as illustrative but not restrictive. The scopes of theembodiments are to be defined by the appended claims rather than theforegoing description. All the changes within the scope of the subjectmatters of the claims and their equivalents are thus to be included inthe scope of the embodiments of the present disclosure.

What is claimed is:
 1. A battery management system, comprising: aninsulation detection circuit, comprising a first isolation module, avoltage division module, a signal generation module, a first samplingpoint and a second sampling point, wherein a first end of the firstisolation module is connected to a positive electrode of a power batteryunder detection, a second end of the first isolation module is connectedto the second sampling point, the signal generation module is connectedto the first sampling point, a first end of the voltage division moduleis connected to the first sampling point, and a second end of thevoltage division module is connected to the second sampling point; amemory configured to store computer codes; and a processor configured toexecute the computer codes to: acquire a first sampled signal from thefirst sampling point and acquire a second sampled signal from the secondsampling point when a preset condition is satisfied, wherein the presetcondition is the signal generation module generates an AC voltage signalof a predetermined frequency; and calculate an insulation resistance ofthe power battery under detection according to the first sampled signaland the second sampled signal.
 2. The battery management system of claim1, wherein the processor is further to: obtain a first voltage amplitudeand a bias voltage of the first sampled signal and a second voltageamplitude of the second sampled signal, and obtain a first instantaneousvoltage of the first sampled signal and a second instantaneous voltageof the second sampled signal at a same moment; calculate a phase shiftof the second sampled signal relative to the first sampled signalaccording to the first voltage amplitude, the bias voltage, the firstinstantaneous voltage, the second voltage amplitude, and the secondinstantaneous voltage; and calculate the insulation resistance of thepower battery under detection according to the phase shift, the firstvoltage amplitude, and the second voltage amplitude.
 3. The batterymanagement system of claim 2, wherein the processor is further to:obtain the first instantaneous voltage at a rising edge of a waveform ofthe first sampled signal and the second instantaneous voltage at arising edge of a waveform of the second sampled signal at the samemoment.
 4. The battery management system of claim 2, wherein theprocessor is further to: calculate the insulation resistance of thepower battery under detection according to the phase shift, the firstvoltage amplitude, the second voltage amplitude, the predeterminedfrequency, a capacitance value of the first isolation module and aresistance value of the voltage division module.
 5. The batterymanagement system of claim 1, wherein the processor is further to:re-determine whether the preset condition is satisfied after apredetermined time period, when the preset condition is not satisfied.6. The battery management system of claim 1, wherein the signalgeneration module is a DDS waveform generator.
 7. The battery managementsystem of claim 1, wherein the AC voltage signal is a sine wave voltagesignal.
 8. The battery management system of claim 1, wherein thepredetermined frequency is less than or equal to 50 kHz.
 9. The batterymanagement system of claim 1, further comprising: a signal amplificationmodule configured to increase a voltage amplitude of the AC voltagesignal.
 10. An insulation detection method to be applied to the batterymanagement system of claim 1, comprising: acquiring a first sampledsignal from the first sampling point and acquiring a second sampledsignal from the second sampling point when a preset condition issatisfied, wherein the preset condition is the signal generation modulegenerates an AC voltage signal of a predetermined frequency; andcalculating an insulation resistance of the power battery underdetection according to the first sampled signal and the second sampledsignal.
 11. The insulation detection method of claim 10, wherein thecalculating an insulation resistance of the power battery underdetection according to the first sampled signal and the second sampledsignal comprises: obtaining a first voltage amplitude and a bias voltageof the first sampled signal and a second voltage amplitude of the secondsampled signal, and obtaining a first instantaneous voltage of the firstsampled signal and a second instantaneous voltage of the second sampledsignal at a same moment; calculating a phase shift of the second sampledsignal relative to the first sampled signal according to the firstvoltage amplitude, the bias voltage, the first instantaneous voltage,the second voltage amplitude, and the second instantaneous voltage; andcalculating the insulation resistance of the power battery underdetection according to the phase shift, the first voltage amplitude, andthe second voltage amplitude.
 12. The insulation detection method ofclaim 11, wherein the obtaining a first instantaneous voltage of thefirst sampled signal and a second instantaneous voltage of the secondsampled signal at a same moment comprises: obtaining the firstinstantaneous voltage at a rising edge of a waveform of the firstsampled signal and the second instantaneous voltage at a rising edge ofa waveform of the second sampled signal at the same moment.
 13. Theinsulation detection method of claim 11, wherein the calculating theinsulation resistance of the power battery under detection according tothe phase shift, the first voltage amplitude, and the second voltageamplitude comprises: calculating the insulation resistance of the powerbattery under detection according to the phase shift, the first voltageamplitude, the second voltage amplitude, the predetermined frequency, acapacitance value of the first isolation module and a resistance valueof the voltage division module.
 14. The insulation detection method ofclaim 10, further comprising: re-determining whether the presetcondition is satisfied after a predetermined time period, when thepreset condition is not satisfied.
 15. The insulation detection methodof claim 10, wherein the AC voltage signal is a sine wave voltagesignal.
 16. The insulation detection method of claim 10, wherein thepredetermined frequency is less than or equal to 50 kHz.
 17. Theinsulation detection method of claim 10, further comprising: increasinga voltage amplitude of the AC voltage signal after the AC voltage signalis generated by the signal generation module.
 18. A non-transitorycomputer readable storage medium having programs or instructions storedon the non-transitory computer readable storage medium, wherein theprograms or the instructions, when executed by a processor, perform theinsulation detection method of claim 1.